f2fs: fix to zero post-eof page

fstest reports a f2fs bug:

generic/363 42s ... [failed, exit status 1]- output mismatch (see /share/git/fstests/results//generic/363.out.bad)
--- tests/generic/363.out 2025-01-12 21:57:40.271440542 +0800
+++ /share/git/fstests/results//generic/363.out.bad 2025-05-19 19:55:58.000000000 +0800
@@ -1,2 +1,78 @@
QA output created by 363
fsx -q -S 0 -e 1 -N 100000
+READ BAD DATA: offset = 0xd6fb, size = 0xf044, fname = /mnt/f2fs/junk
+OFFSET GOOD BAD RANGE
+0x1540d 0x0000 0x2a25 0x0
+operation# (mod 256) for the bad data may be 37
+0x1540e 0x0000 0x2527 0x1
...
(Run 'diff -u /share/git/fstests/tests/generic/363.out /share/git/fstests/results//generic/363.out.bad' to see the entire diff)
Ran: generic/363
Failures: generic/363
Failed 1 of 1 tests

The root cause is user can update post-eof page via mmap [1], however, f2fs
missed to zero post-eof page in below operations, so, once it expands i_size,
then it will include dummy data locates previous post-eof page, so during
below operations, we need to zero post-eof page.

Operations which can include dummy data after previous i_size after expanding
i_size:
- write
- mapwrite [1]
- truncate
- fallocate
* preallocate
* zero_range
* insert_range
* collapse_range
- clone_range (doesn’t support in f2fs)
- copy_range (doesn’t support in f2fs)

[1] https://man7.org/linux/man-pages/man2/mmap.2.html 'BUG section'

Cc: [e-mail]
Signed-off-by: Chao Yu <[e-mail]>
Reviewed-by: Zhiguo Niu <[e-mail]>
Signed-off-by: Jaegeuk Kim <[e-mail]>

fs/f2fs/file.c

···
 #include <trace/events/f2fs.h>
 #include <uapi/linux/f2fs.h>
 
+static void f2fs_zero_post_eof_page(struct inode *inode, loff_t new_size)
+{
+	loff_t old_size = i_size_read(inode);
+
+	if (old_size >= new_size)
+		return;
+
+	/* zero or drop pages only in range of [old_size, new_size] */
+	truncate_pagecache(inode, old_size);
+}
+
 static vm_fault_t f2fs_filemap_fault(struct vm_fault *vmf)
 {
 	struct inode *inode = file_inode(vmf->vma->vm_file);
···
 
 	f2fs_bug_on(sbi, f2fs_has_inline_data(inode));
 
+	filemap_invalidate_lock(inode->i_mapping);
+	f2fs_zero_post_eof_page(inode, (folio->index + 1) << PAGE_SHIFT);
+	filemap_invalidate_unlock(inode->i_mapping);
+
 	file_update_time(vmf->vma->vm_file);
 	filemap_invalidate_lock_shared(inode->i_mapping);
+
 	folio_lock(folio);
 	if (unlikely(folio->mapping != inode->i_mapping ||
 			folio_pos(folio) > i_size_read(inode) ||
···
 		f2fs_down_write(&fi->i_gc_rwsem[WRITE]);
 		filemap_invalidate_lock(inode->i_mapping);
 
+		if (attr->ia_size > old_size)
+			f2fs_zero_post_eof_page(inode, attr->ia_size);
 		truncate_setsize(inode, attr->ia_size);
 
 		if (attr->ia_size <= old_size)
···
 	ret = f2fs_convert_inline_inode(inode);
 	if (ret)
 		return ret;
+
+	filemap_invalidate_lock(inode->i_mapping);
+	f2fs_zero_post_eof_page(inode, offset + len);
+	filemap_invalidate_unlock(inode->i_mapping);
 
 	pg_start = ((unsigned long long) offset) >> PAGE_SHIFT;
 	pg_end = ((unsigned long long) offset + len) >> PAGE_SHIFT;
···
 	f2fs_down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
 	filemap_invalidate_lock(inode->i_mapping);
 
+	f2fs_zero_post_eof_page(inode, offset + len);
+
 	f2fs_lock_op(sbi);
 	f2fs_drop_extent_tree(inode);
 	truncate_pagecache(inode, offset);
···
 	ret = filemap_write_and_wait_range(mapping, offset, offset + len - 1);
 	if (ret)
 		return ret;
+
+	filemap_invalidate_lock(mapping);
+	f2fs_zero_post_eof_page(inode, offset + len);
+	filemap_invalidate_unlock(mapping);
 
 	pg_start = ((unsigned long long) offset) >> PAGE_SHIFT;
 	pg_end = ((unsigned long long) offset + len) >> PAGE_SHIFT;
···
 	/* avoid gc operation during block exchange */
 	f2fs_down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
 	filemap_invalidate_lock(mapping);
+
+	f2fs_zero_post_eof_page(inode, offset + len);
 	truncate_pagecache(inode, offset);
 
 	while (!ret && idx > pg_start) {
···
 	err = f2fs_convert_inline_inode(inode);
 	if (err)
 		return err;
+
+	filemap_invalidate_lock(inode->i_mapping);
+	f2fs_zero_post_eof_page(inode, offset + len);
+	filemap_invalidate_unlock(inode->i_mapping);
 
 	f2fs_balance_fs(sbi, true);
 
···
 	err = file_modified(file);
 	if (err)
 		return err;
+
+	filemap_invalidate_lock(inode->i_mapping);
+	f2fs_zero_post_eof_page(inode, iocb->ki_pos + iov_iter_count(from));
+	filemap_invalidate_unlock(inode->i_mapping);
 	return count;
 }